Various processes require that a material be treated at an elevated temperature with a fluid. This treatment may occur at a high temperature provided by the incoming material, which may be continually input and removed from the equipment in a continuous flowthrough process rather than a batch process. In some treatment processes, it is important that the heat loss from the incoming material be minimized. The treatment system envisioned by this invention is substantially complicated by the fact that the treating fluid is highly deleterious to the desired housing material for the process chamber, at least at the elevated temperatures at which the treatment is occurring.
Those skilled in the cracking of hydrocarbon feedstock have long recognized the value of various solid catalyst to yield more valuable end products. These catalysts typically may be manufactured from various synthetic crystalline materials, and are utilized in powder form with particle sizes ranging from 1 to 100 microns. The solid catalyst become contaminated or poisoned by "metals" during the hydrocarbon conversion, with the term "metals" referring to contaminants in the form of either free metals or relatively non-volatile compounds. U.S. Pat. No. 3,140,253 and U.S. Pat. No. Re. 27,639 generally disclose techniques for preparing a suitable catalyst for cracking hydrocarbon feedstocks.
Various techniques have been devised for removing metals from the hydrocarbon conversion catalyst so that the catalyst can be returned to the cracking operation. One commonly used technique is to chlorinate a contaminated catalyst at elevated temperatures. According to the technique described in detail in U.S. Pat. No. 4,686,197, the contaminated catalyst is demetalized by contacting the catalyst with at least one chlorine-containing component. Chlorination can be effective to remove vanadium from the catalyst, and also for placing nickel poisons into a form soluble in an aqueous solution. After chlorination and washing, the demetalized catalyst may then be returned to a fluid bed reactor vessel for cracking hydrocarbons.
As disclosed in the '197 patent, contaminated catalyst from the fluid bed catalytic cracking operation may be passed through an initial sulfiding process for enhancing the removal of nickel and vanadium during the subsequent chlorination and washing processes. During the sulfiding step, the poisoned catalyst is contacted with elemental sulfur vapors, such as H.sub.2 S. According to the prior art, this sulfiding step is preferably performed in an in-line or continuous flow-through process by passing the heated catalyst into a sealed reactor having metal walls. H.sub.2 S is introduced into the bottom of the reactor and passed upward through the fluid bed formed by the catalyst. Although the sulfiding process preferably occurred at temperatures above 1200.degree. F., it is difficult to maintain the catalyst at this temperature, even if the walls of the metal reactor are covered with a reasonable layer of insulation.
At temperatures in excess of 800.degree. F., H.sub.2 S becomes highly corrosive to most metals, and thus corrosion of the sulfider walls substantially limited the expected life of the sulfider. In an effort to try to raise the temperature of the sulfiding operation, heaters were placed external of and in physical contact with the metal sulfider walls, with the insulation layer then being placed outward of the heaters. Although this procedure had the desired effect of reducing the heat loss from the catalyst during the sulfiding process, it had the undesirable effect of further increasing the corrosion of the stainless steels walls which formed the sulfider, and accordingly further reduced the life of the sulfider. Utilizing the above technique, it has been found that a sulfider with one-half inch stainless steel walls had a wall reduction of approximately 50% after operating the sulfider for approximately six to eight months, and that the integrity of the remaining thickness of the wall was such that the sulfider effectively had to be rebuilt. The maintenance and construction of the sulfiders is thus a significant cost of the overall catalyst demetalization process, and improved methods and techniques are therefore required to enhance the life of the sulfider and lower the overall process of demetalizing the catalyst.
The disadvantages of the prior art are overcome by the present invention, and improved methods and apparatus are hereinafter disclosed for substantially minimizing heat loss from the treatment process which includes a corrosive gas or liquid deleterious to the material of the treatment housing at the elevated temperatures. The techniques of the present invention are particularly well suited for manufacturing an improved sulfider used in hydrocarbon cracking operations to assist in demetalizing catalysts by subjecting the contaminated catalyst to a sulfur-containing gas.